All animals start life as a single cell, the fertilized egg. Through the process of embryonic development, the fertilized egg divides into hundreds of different cell types arranged in highly complex and well-organized patterns. The long term objective of the proposed research is to apply modem molecular and embryological techniques to address an age-old question: how are the fundamental body plans in humans and animals formed? The specific goal of this research is to identify the processes and molecules that are involved in orchestrating the first steps of vertebrate embryonic development. It is known that some of the information required for development is put into the egg as maternal messenger RNA (mRNA) molecules that initiate complex patterns of gene expression. It is also known in Xenopus that a small group of specialized cells in the dorsal region of an embryo plays a central role in development, by providing the instructions necessary to 'organize' the rest of the embryo into a normally formed animal. A class of mRNA molecules that are found only in cells of this specialized dorsal region of the embryo has been cDNA cloned and is being characterized. The research proposed here has two specific aims. First, by analyzing the distribution of mRNA species in different regions of the embryo and by following the fate of modified mRNAs microinjected into embryos, it will identify the cellular and molecular mechanisms that result in the localization of this special class of maternal mRNAs. This analysis will greatly increase our ability to trace the biological cascade from fertilization to vertebrate pattern formation. Second it is now possible using microinjection of antisense oligonucleotides to specifically eliminate a maternal mRNA species within an oocyte, then to mature and fertilize the egg in vitro to assess the effects on the developing embryo. This powerful molecular embryology technique will be used to investigate the function(s) of these dorsally localized maternal mRNAs in development In light of the unique 'organizing' role of the dorsal region, it is likely that this analysis will increase our understanding of human congenital malformations on a molecular level. This study will greatly deepen our understanding of gene regulation and the fundamental mechanisms underlying vertebrate development, cellular differentiation and pattern formation.